4,458 research outputs found
Controlling the Kondo Effect in CoCu_n Clusters Atom by Atom
Clusters containing a single magnetic impurity were investigated by scanning
tunneling microscopy, spectroscopy, and ab initio electronic structure
calculations. The Kondo temperature of a Co atom embedded in Cu clusters on
Cu(111) exhibits a non-monotonic variation with the cluster size. Calculations
model the experimental observations and demonstrate the importance of the local
and anisotropic electronic structure for correlation effects in small clusters.Comment: 4 pages, 4 figure
Broad-band X-Ray Spectra of the Black Hole Candidate GRO J1655-40
We present broad-band (2 keV to 2 MeV) X-ray spectra of GRO J1655-40, a
luminous X-ray transient and occasional source of relativistic radio jets,
obtained with RXTE and OSSE. In one observation, the luminosity is found to be
18% of the Eddington limit, which is one of the highest luminosities ever
observed from GRO J1655-40. For this observation, we find that an adequate fit
is obtained when a broad iron line and a reflection component are added to a
model consisting of a power-law plus a soft excess component. The 95%
confidence lower limit on the rms line width is 0.86 keV. The power-law
component has a photon index of 2.72 and extends to at least 800 keV without a
cutoff. After this observation, a significant drop in the (5-12 keV)/(1.5-5
keV) hardness ratio occurred on a timescale less than 2 hours. From an RXTE
observation of GRO J1655-40 made after the hardness transition, we find that
the power-law index is harder (2.415 +/- 0.011), the flux of the power-law
component is lower, and the total luminosity is 10% of the Eddington limit. The
change in the power-law component is consistent with the correlation between
the spectral index and power-law flux previously reported for GRO J1655-40.Comment: 20 pages, 5 figures, Accepted for publication in the Astrophysical
Journa
Non-Causal Tracking by Deblatting
Tracking by Deblatting stands for solving an inverse problem of deblurring
and image matting for tracking motion-blurred objects. We propose non-causal
Tracking by Deblatting which estimates continuous, complete and accurate object
trajectories. Energy minimization by dynamic programming is used to detect
abrupt changes of motion, called bounces. High-order polynomials are fitted to
segments, which are parts of the trajectory separated by bounces. The output is
a continuous trajectory function which assigns location for every real-valued
time stamp from zero to the number of frames. Additionally, we show that from
the trajectory function precise physical calculations are possible, such as
radius, gravity or sub-frame object velocity. Velocity estimation is compared
to the high-speed camera measurements and radars. Results show high performance
of the proposed method in terms of Trajectory-IoU, recall and velocity
estimation.Comment: Published at GCPR 2019, oral presentation, Best Paper Honorable
Mention Awar
Continuous feedback on a quantum gas coupled to an optical cavity
We present an active feedback scheme acting continuously on the state of a
quantum gas dispersively coupled to a high-finesse optical cavity. The quantum
gas is subject to a transverse pump laser field inducing a self-organization
phase transition, where the gas acquires a density modulation and photons are
scattered into the resonator. Photons leaking from the cavity allow for a
real-time and non-destructive readout of the system. We stabilize the mean
intra-cavity photon number through a micro-processor controlled feedback
architecture acting on the intensity of the transverse pump field. The feedback
scheme can keep the mean intra-cavity photon number constant, in
a range between and , and
for up to 4 s. Thus we can engage the stabilization in a regime where the
system is very close to criticality as well as deep in the self-organized
phase. The presented scheme allows us to approach the self-organization phase
transition in a highly controlled manner and is a first step on the path
towards the realization of many-body phases driven by tailored feedback
mechanisms
Improved part-of-speech prediction in suffix analysis
MotivationPredicting the part of speech (POS) tag of an unknown word in a sentence is a significant challenge. This is particularly difficult in biomedicine, where POS tags serve as an input to training sophisticated literature summarization techniques, such as those based on Hidden Markov Models (HMM). Different approaches have been taken to deal with the POS tagger challenge, but with one exception--the TnT POS tagger--previous publications on POS tagging have omitted details of the suffix analysis used for handling unknown words. The suffix of an English word is a strong predictor of a POS tag for that word. As a pre-requisite for an accurate HMM POS tagger for biomedical publications, we present an efficient suffix prediction method for integration into a POS tagger.ResultsWe have implemented a fully functional HMM POS tagger using experimentally optimised suffix based prediction. Our simple suffix analysis method, significantly outperformed the probability interpolation based TnT method. We have also shown how important suffix analysis can be for probability estimation of a known word (in the training corpus) with an unseen POS tag; a common scenario with a small training corpus. We then integrated this simple method in our POS tagger and determined an optimised parameter set for both methods, which can help developers to optimise their current algorithm, based on our results. We also introduce the concept of counting methods in maximum likelihood estimation for the first time and show how counting methods can affect the prediction result. Finally, we describe how machine-learning techniques were applied to identify words, for which prediction of POS tags were always incorrect and propose a method to handle words of this type.Availability and implementationJava source code, binaries and setup instructions are freely available at http://genomes.sapac.edu.au/text_mining/pos_tagger.zip.Mario Fruzangohar, Trent A. Kroeger, David L. Adelso
Gamma-Ray Spectral States of Galactic Black Hole Candidates
OSSE has observed seven transient black hole candidates: GRO J0422+32,
GX339-4, GRS 1716-249, GRS 1009-45, 4U 1543-47, GRO J1655-40, and GRS 1915+105.
Two gamma-ray spectral states are evident and, based on a limited number of
contemporaneous X-ray and gamma-ray observations, these states appear to be
correlated with X-ray states. The former three objects show hard spectra below
100 keV (photon number indices Gamma < 2) that are exponentially cut off with
folding energy ~100 keV, a spectral form that is consistent with thermal
Comptonization. This "breaking gamma-ray state" is the high-energy extension of
the X-ray low, hard state. In this state, the majority of the luminosity is
above the X-ray band, carried by photons of energy ~100 keV. The latter four
objects exhibit a "power-law gamma-ray state" with a relatively soft spectral
index (Gamma ~ 2.5-3) and no evidence for a spectral break. For GRO J1655-40,
the lower limit on the break energy is 690 keV. GRS 1716-249 exhibits both
spectral states, with the power-law state having significantly lower gamma-ray
luminosity. The power-law gamma-ray state is associated with the presence of a
strong ultrasoft X-ray excess (kT ~ 1 keV), the signature of the X-ray high,
soft (or perhaps very high) state. The physical process responsible for the
unbroken power law is not well understood, although the spectra are consistent
with bulk-motion Comptonization in the convergent accretion flow.Comment: 27 pages, 3 figures, uses aaspp.sty and psfig.st
Cumulative reproductive costs on current reproduction in a wild polytocous mammal
Funding Information MarieâCurie Fellowship UCLA Rocky Mountain Biological Laboratory Research Fellowship NSF. Grant Numbers: IDBRâ0754247, DEBâ1119660, DBI 0242960, DBI 0731346 Natural Environment Research Council. Grant Number: NE/L50175X/1 National Geographic SocietyPeer reviewedPublisher PD
Older mothers produce more successful daughters
Acknowledgements Marmots were studied under UCLA research protocol ARC 2001-191-01 (approved by the UCLA Animal Care Committee on 13 May 2002 and renewed annually). Permits were issued by the Colorado Division of Wildlife. We are thankful to all marmoteers who contributed to data collection. S.B.K. was supported by the Natural Environment Research Council, J.G.A.M. by a Marie-Curie Fellowship, and D.T.B by the National Geographic Society, UCLA (Faculty Senate and the Division of Life Sciences), a Rocky Mountain Biological Laboratory research fellowship, and the NSF (IDBR-0754247, DEB1119660 and DEB-1557130 to D.T.B., and DBI 0242960, DBI-0731346 and REU1226713 to the Rocky Mountain Biological Laboratory).Peer reviewedPostprin
Strong social relationships are associated with decreased longevity in a facultatively social mammal
Data accessibility. Data are available from the Dryad Digital Repository at: https://doi.org/10.5061/dryad.h8n7p [40]. D.T.B. was supported by the National Geographic Society, UCLA (Faculty Senate and the Division of Life Sciences), a Rocky Mountain Biological Laboratory research fellowship and by the NSF (IDBR-0754247, and DEB-1119660 and 1557130 to D.T.B., as well as DBI-0242960, 0731346 and 1226713 to the Rocky Mountain Biological Laboratory).Peer reviewedPostprin
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